- With 25 subjects per group this study will have an 80% power to detect a difference in continuous variables equivalent to 80% of a standard deviation with a 2-sided p-value of 0.05. Based on the assumption of normality, a reduction of one standard deviation would be equivalent to about 24%, therefore a reduction of .8 of a standard deviation would be approximately equivalent to a 20% reduction. A difference of this size is perceived to be of clinical importance. Repeat measures analysis will further increase the power of this study although until between measures variability can be assessed, it is unsure by how much.